The present invention relates to an AC plasma display panel used for image display in a television receiver, a computer monitor, or the like.
A conventional AC plasma display panel (hereinafter referred to as a xe2x80x9cpanelxe2x80x9d) is shown in FIG. 6. On a first insulating substrate 1, a plurality of sustain electrodes 4 and a plurality of scanning electrodes 5, which are covered with a dielectric layer 2 and a protective film 3, are provided alternately in parallel. A plurality of data electrodes 7 are provided on a second insulating substrate 6. Between respective data electrodes 7, a plurality of separation walls 8 are provided in parallel to the data electrodes 7. Phosphors 9 are provided on the data electrodes 7 and side faces of the separation walls 8. The first insulating substrate 1 and the second insulating substrate 6 are positioned opposing each other so that the sustain electrodes 4 and the scanning electrodes 5 are orthogonal to the data electrodes 7. Each sustain electrode 4 includes a transparent electrode 41 and a bus-bar 42 formed on the transparent electrode 41. Similarly, each scanning electrode 5 includes a transparent electrode 51 and a bus-bar 52 formed on the transparent electrode 51.
Generally, since a transparent electrode formed of ITO (Indium Tin Oxide) or the like has a high resistance, a bus-bar formed of silver or the like is superposed on the transparent electrode, thus lowering the resistance in an electrode as a whole. Therefore, the resistances per unit length of the sustain electrode 4 and the scanning electrode 5 depend on the resistance of the bus-bars 42 and 52. Thus, the line width of the bus-bar 42 of the sustain electrode 4 and that of the bus-bar 52 of the scanning electrode 5 are made to be approximately the same, thus setting the resistance per unit length of the sustain electrode 4 and that of the scanning electrode 5 to be approximately the same. Further, on both the adjacent sides of all the scanning electrodes 5, the sustain electrodes 4 are disposed. Display is carried out by sustain discharges in two places between respective scanning electrodes 5 and sustain electrodes 4 on both the adjacent sides thereof.
As shown in FIG. 7, the electrodes in this conventional panel include M rows of scanning electrodes SCN1 to SCNM and M+1 rows of sustain electrodes SUS1 to SUSM+1, which are arranged in the row direction. In the column direction, N columns of data electrodes D1 to DN are arranged. The intersections of the respective data electrodes and the respective sets of scanning electrodes and sustain electrodes on both adjacent sides thereof function as discharge cells C11 to CMN. The discharge cells C11 to CMN are arranged in a matrix form of Mxc3x97N. The scanning electrodes SCN1 to SCNM are connected to a driving circuit at their left ends and the sustain electrodes SUS1 to SUSM+1 are connected to the driving circuit at their right ends, which is not shown in the figure.
A method of driving this conventional panel is described using a diagram showing a timing chart of an operation driving waveform shown in FIG. 8.
Initially, in a write period, all the sustain electrodes SUS1 to SUSM+1 are maintained at a voltage of 0. In scanning of the first row by a scanning electrode SCN1, a positive write pulse voltage of +Vw is applied to a designated data electrode Dj (j indicates one or more integers of 1 to N) that is selected from the data electrodes D1 to DN and corresponds to a discharge cell to be operated so as to emit light, and a negative scan pulse voltage of xe2x88x92Vs is applied to the scanning electrode SCN1. This causes a write discharge in a discharge cell C1j at the intersection of the designated data electrode Dj and the scanning electrode SCN1. This write discharge induces discharges between the scanning electrode SCN1 and respective half portions of the sustain electrodes SUS1 and SUS2 facing the scanning electrode SCN1. In the discharge cell C1j in which the write discharges have occurred, positive electric charges are stored at the surface of the protective film 3 on the scanning electrode SCN1, and negative electric charges at the surface of the protective film 3 on the respective half portions of the sustain electrodes SUS1 and SUS2.
Next, in scanning of the second row by a scanning electrode SCN2, a positive write pulse voltage of +Vw is applied to a designated data electrode Dj that is selected from the data electrodes D1 to DN and corresponds to a discharge cell to be operated so as to emit light, and a negative scan pulse voltage of xe2x88x92Vs is applied to the scanning electrode SCN2. This causes a write discharge in a discharge cell C2j at the intersection of the designated data electrode Dj and the scanning electrode SCN2. This write discharge induces discharges between the scanning electrode SCN2 and respective half portions of the sustain electrodes SUS2 and SUS3 facing the scanning electrode SCN2. In the discharge cell C2j in which the write discharges have occurred, positive electric charges are stored at the surface of the protective film 3 on the scanning electrode SCN2, and negative electric charges at the surface of the protective film 3 on the respective half portions of the sustain electrodes SUS2 and SUS3.
Successively, the same scanning operation is carried out for all remaining rows up to the scanning electrode SCNM in the M row. Thus, the same predetermined electric charges as described above are stored at the surface of the protective film 3.
In the subsequent sustain period, initially a negative sustain pulse voltage of xe2x88x92Vm is applied to all the sustain electrodes SUS1 to SUSM+1. Thus, in a discharge cell Cij (i indicates one or more integers selected from 1 to M) in which the write discharges have occurred, the voltage between the surface of the protective film 3 on a scanning electrode SCNi and the surface of the protective film 3 on sustain electrodes SUSi or SUSi+1 is the sum of the negative sustain pulse voltage of xe2x88x92Vm, the positive electric charges at the surface of the protective film 3 on the scanning electrode SCNi, and the negative electric charges at the surface of the protective film 3 on the sustain electrodes SUSi or SUSi+1, which exceeds the discharge starting voltage. Therefore, sustain discharges start between the scanning electrode SCNi and the sustain electrodes SUSi and SUSi+1. As a result, the electric charges stored at the surface of the protective film 3 are reversed and thus negative electric charges are stored at the surface of the protective film 3 on the scanning electrode SCNi and positive electric charges at the surface of the protective film 3 on the sustain electrodes SUSi and SUSi+1. Successively, the negative sustain pulse voltage of xe2x88x92Vm is applied to all the scanning electrodes SCN1 to SCNM and all the sustain electrodes SUS1 to SUSM alternately. Thus, in the discharge cell Cij in which the write discharges have occurred, sustain discharges occur successively between the scanning electrode SCNi and the sustain electrodes SUSi and SUSi+1. Light emissions caused by those sustain discharges are used for display.
In the subsequent erase period, a negative narrow-width erase pulse voltage of xe2x88x92Ve is applied to all the sustain electrodes SUS1 to SUSM+1. This causes erase discharges to terminate the sustain discharges. With the above-mentioned operations, one picture is displayed in the panel.
In such display of one picture, only light emissions with a certain constant luminance can be used for the display. Therefore, when a gray-scale image is to be displayed as in image display for a television, the display period of one picture is set to be one subfield, and during {fraction (1/60)} second, which is the duration of one field, subfields, each of which has a different luminance of light emission used for display, are repeated plural times. For example, if a reference luminance is B0, by using one field consisting of eight subfields sub1, sub2, sub3, . . . , sub8 in which display luminances are 20xc3x97B0, 21xc3x97B0, 22xc3x97B0, . . . , 27xc3x97B0 respectively, a display having 28=256 shades of gray can be carried out.
In the above-mentioned conventional panel, however, in the case of a partial display, the difference in luminance may occur on the right and left sides of a screen, thus causing unevenness in display luminance, which has been a problem. Furthermore, discharge cells other than those intended to emit light may be operated to emit light due to error discharges, thus causing error display, which also has been a problem. These problems are explained as follows.
FIG. 9 shows an array of the electrodes in the first to third rows shown in the electrode array diagram in FIG. 7. FIG. 9(a) shows a state in which sustain discharges are occurring in three discharge cells C1j, C2j, and C3j positioned in the first to third rows in the j column. FIG. 9(b) shows a state in which sustain discharges are occurring only in one discharge cell C2j positioned in the second row in the j column. In each diagram, arrows indicate discharge currents flowing in the scanning electrodes SCN1, SCN2and SCN3 and the sustain electrodes SUS1, SUS2, SUS3, and SUS4. In this case, suppose the resistance per unit length of the scanning electrodes SCN1 to SCNM and the sustain electrodes SUS1 to SUSM+1 is R (xcexa9/m), lengths of the electrodes are L (m), and the center positions of the discharge cells C1j, C2j, and C3j measured from the left side of the panel are x (m). Further, suppose the sum of discharge currents caused by the respective discharges occurring in two places in respective discharge cells, i.e. the discharges between the respective scanning electrodes and sustain electrodes on both the adjacent sides thereof is I (A), and the center position of the discharge cell Ci1 at the left end of the panel is expressed as x=0. Further, assuming that V1a and V1b, V2a and V2b, and V3a and V3b represent the voltages applied to respective discharging places in the discharge cells C1j, C2j, and C3j when a voltage of 0 and a sustain pulse voltage of xe2x88x92Vm are applied to the scanning electrodes SCN1 to SCNM and the sustain electrodes SUS1 to SUSM+1 respectively, these voltages are described as follows.
In the case shown in FIG. 9(a), as is apparent from the diagram, since the discharge currents from the scanning electrodes SCN1 and SCN2 (I/2 each) are added in the sustain electrode SUS2, the quantity of discharge current flowing in the sustain electrode SUS2 is twice the discharge current of I/2. Similarly, the discharge currents from the scanning electrodes SCN2 and SCN3 (I/2 each) are added in the sustain electrode SUS3, and therefore the quantity of discharge current flowing in the sustain electrode SUS3 is twice the discharge current of I/2. Therefore, V1b=V2a=V2b=V3a=Vmxe2x88x92Ixc3x97Rxc3x97xxe2x88x922xc3x97I/2xc3x97Rxc3x97(Lxe2x88x92x)=Vmxe2x88x92Ixc3x97Rxc3x97L. The voltages applied to respective discharging places in the discharge cells C1j, C2j, and C3j are independent of the positions x of the discharge cells. On the other hand, the discharge current flowing in the respective sustain electrodes SUS1 and SUS4 is only the discharge current of I/2 from the respective scanning electrodes SCN1 and SCN3. Therefore, V1a=V3b=Vmxe2x88x92Ixc3x97Rxc3x97xxe2x88x92I/2xc3x97Rxc3x97(Lxe2x88x92x)=Vmxe2x88x92Ixc3x97Rxc3x97(L+x)/2. The voltage applied to one of the two discharging places in each discharge cell is different depending on the position x of the discharge cell. In other words, the discharge intensity varies depending on the positions x of the discharge cells. Thus, the discharges in the two discharging places in the discharge cell C2j always have the same intensity independent of the position x of the discharge cell C2j, while with respect to the discharge cells C1j and C3j, the discharge intensity in one of the two discharging places in the respective discharge cells C1j and C3j varies depending on their positions x. When the discharge cells C1j and C3j are positioned at the left end of the panel, i.e. j=1, x=0 holds. Therefore, V1a=V3b=Vmxe2x88x92Ixc3x97Rxc3x97L/2. When the discharge cells C1j and C3j are positioned at the right end of the panel, i.e. j=N, x=L holds. Therefore, V1a=V3b=Vmxe2x88x92Ixc3x97Rxc3x97L. Thus, when the discharge cells C1j and C3j are positioned at the right end of the panel, the voltage applied to them is lower than that applied to them when they are positioned at the left end of the panel, and thus the discharge intensity in those discharge cells is decreased.
In the case shown in FIG. 9(b), from the same calculation as described above, both of the voltages V2a and V2b applied to the two discharging places in the discharge cell C2j are expressed as V2a=V2b=Vmxe2x88x92Ixc3x97Rxc3x97(L+x)/2. Therefore, the voltage applied to the two discharging places in the discharge cell C2j varies depending on the position x of the discharge cell C2j, which means that the discharge intensity varies. In other words, when the discharge cell C2j is positioned at the right end of the panel, the discharge intensity of the discharge cell C2j further decreases compared to that when it is positioned at the left end of the panel.
For simplification, the above description was directed to one discharge cell in the respective first to third rows. In a practical panel, however, the distribution of discharge cells to be operated so as to emit light may be scattered, and in such a discharge intensity varies depending on the positions of the discharge cells. Therefore, in the case of partial display in the panel, the luminance varies on the right and left sides of the panel, thus causing unevenness in display luminance, which has been a problem.
Next, FIGS. 10(a), 10(b), and 10(c) show sectional views taken along line A-Axe2x80x2 shown in FIG. 6. These figures illustrate the manner of sustain discharges in a sustain period. These figures show the case where in the sustain period, a sustain pulse voltage is applied to the scanning electrodes SCN1 to SCNM and the sustain electrodes SUS1 to SUSM+1 alternately, and the sustain discharges occur only between the scanning electrode SCN2 and the sustain electrodes SUS2 and SUS3 on both adjacent sides thereof. The solid-line arrows in FIG. 10(a) indicate initial sustain discharges in the sustain period that occur between the scanning electrode SCN2 and the sustain electrodes SUS2 and SUS3 on both adjacent sides thereof. Due to these sustain discharges, positive electric charges are stored at the surface of the protective layer 3 on the scanning electrode SCN2, and negative electric charges are stored at the surface of the protective layer 3 on respective half portions of the sustain electrodes SUS2 and SUS3 facing the scanning electrode SCN2. A subsequent sustain pulse voltage is applied to scanning electrodes and sustain electrodes alternately, thus repeating the discharges indicated with the solid-line arrows. In this case, positive electric charges and negative electric charges are stored alternately and reversibly at the surface of the protective film 3 on respective half portions of the sustain electrodes SUS2 and SUS3 facing the scanning electrode SCN2. However, when the sustain discharges continue, the electric discharges stored at the surface of the protective film 3 on respective half portions of the sustain electrodes SUS2 and SUS3 facing the scanning electrode SCN2 spread over the entire surface of the protective film 3 on the sustain electrodes SUS2 and SUS3. Therefore, as shown with broken-line arrows in FIG. 10(a), the sustain discharges extend to occur between the scanning electrode SCN2 and the entire surface on the sustain electrodes SUS2 and SUS3. As a result, as shown with the solid-line arrows in FIG. 10(b), the sustain discharges also occur between the scanning electrode SCN1 and the sustain electrode SUS2 and between the sustain electrode SUS3 and the scanning electrode SCN3.
Further, when the sustain discharges continue, the discharges that have occurred between the scanning electrode SCN1 and the sustain electrode SUS2 and between the sustain electrode SUS3 and the scanning electrode SCN3 extend to the entire surface on the scanning electrode SCN1 and the entire surface on the scanning electrode SCN3 as shown with the broken-line arrows in FIG. 10(b). In this way, the discharges extend successively. As a result, the sustain discharges that should occur only between the scanning electrode SCN2 and the sustain electrodes SUS2 and SUS3 on both adjacent sides thereof extend to occur between all the scanning electrodes SCN1 to SCNM and all the sustain electrodes SUS1 to SUSM+1 as shown in FIG. 10(c). In other words, display cells other than those intended to emit light are operated to emit light due to error discharges, thus causing error display, which has been a problem.
The above description was directed only to the sustain discharge in the second row. However, the above-mentioned error discharges also occur in sustain discharges other than those in the second row or in sustain discharges in a plurality of rows.
The present invention is intended to solve such problems and provides an AC plasma display panel in which display with a uniform luminance over its entire screen can be achieved and the occurrence of error display due to error discharges can be suppressed.
An AC plasma display panel of the present invention includes: a first insulating substrate and a second insulating substrate, which are arranged opposing each other; a scanning/sustain-electrode group including a plurality of sets of a scanning electrode and a sustain electrode that are arranged in parallel to each other on the first insulating substrate; a dielectric layer covering the scanning/sustain-electrode group; and a plurality of data electrodes orthogonal to and opposing the scanning electrode and the sustain electrodes, which are provided on the second insulating substrate. In the AC plasma display panel, discharges between the scanning electrode and the sustain electrode allow phosphors to emit light. Each of the plurality of sets includes, as a unit, the scanning electrode and the sustain electrodes on both sides of the scanning electrode. The plurality of sets are separated from one another.
According to this configuration, it is possible to suppress the extension of sustain discharges in a certain discharge cell to the adjacent discharge cells.
It is preferable that the width of the sustain electrodes is approximately half the width of the scanning electrode. Furthermore, it is preferable that a resistance per unit length of the sustain electrodes is approximately twice as high as that of the scanning electrode.